Primate intelligence

Out of the mist

Is Rollie an exception, or are all gorillas as clever?

WHEN it comes to researching intelligence in primates, chimpanzees and orang-utans get all the attention. Chimpanzees have even been shown to outperform humans in memory tests and orang-utans have demonstrated impressive mathematical abilities. Gorillas, by comparison, have been left to one side because, well, let's say they have been seen as the not-so-bright cousins. But that view of gorillas may not be deserved.

The perceptions of gorillas are beginning to change as primatologists get to know more about Rollie (pictured), a ten-year-old female who lives at Lincoln Park Zoo in Chicago. This is a gorilla who is capable of doing a lot more than anyone expected. In a recent study Rollie showed that she is rather good at learning to put discrete items into a list, a skill that is used by people to memorise phone numbers, interpret calendars and, most importantly of all, acquire and process language.

Listing young

Studying list-making skills in humans can be confounded by the fact that people know a lot about lists because they are confronted with them from a very young age. This early introduction is thought to shape their list-making ability, but it makes it impossible to study that ability in its raw, uninfluenced form. As a result, psychologists have embraced a comparative approach and look for the underlying skills in animals that have never before been exposed to lists.

Many species, ranging from pigeons to monkeys, have shown that they can make or learn lists. But Steve Ross, a primatologist at Lincoln Park Zoo, wanted to explore this behaviour further and found that there were no data on sequential learning in gorillas. In fact, he found that there was scarcely any information on gorilla cognition at all.

Surprised by this gap in the literature, Mr Ross decided to test one of Lincoln Park Zoo's gorillas with a simple list-learning task using a 42-inch touch-screen computer that was usually reserved for work with chimpanzees. This is how Rollie came into the picture.

During the study, Rollie voluntarily went into the area equipped with the screen. When she approached it a set of randomly positioned numbers appeared. Her task was to select each numeral in the correct order. If she correctly completed the entire sequence she received a small gift in the form of a sugar-free sweet. If she did not correctly complete the sequence she received no reward.

At the start the tasks were easy; she simply had to select a “1” before a “2” to get the sweet. Now, after some two years and about 25 hours in front of the computer screen, she is working on seven numerals and getting things right 35% of the time. The likelihood of getting such a sequence right by chance is less than 1 in 5,000.

Watch out, monkeys

Mr Ross told the 22nd International Primatological Society Congress held recently in Edinburgh that Rollie has advanced to longer and more complex list-related tasks faster than many other species that have been studied. For an example, it took her 18 sessions to graduate to five numerals. Many monkeys needed over 50 sessions to get there. Poor old lemurs required over 500 sessions.

However, comparing data from various studies can be unreliable because slightly different methods may be used. So to be certain that Rollie was as talented as she seemed to be, Mr Ross ran a bright chimp called Optimus Prime through the same process and compared the results. He found that Rollie completed her tasks in half the time that Optimus needed.

While it is a remarkable demonstration, a lot more gorillas need to be studied before broad conclusions can be drawn. Mr Ross admits that Rollie could just be an exceptional gorilla—or one that is highly motivated by jelly sweets.